This invention relates to apparatus for the collection and conversion of solar energy.
The possibility of utilizing solar energy as a direct source of useful thermal energy has long been appreciated, but for the most part has resisted efforts at practical exploitation in many applications. Of course, merely by its shining upon the earth the sun produces a warming effect, and the rate of delivery of calories from the sun to the earth on a bright day is very great. However, the heating is distributed over such a large area that the temperature rise produced in the irradiated area is only moderate. For many important purposes what is needed is a very high temperature, e.g. 600.degree. to 1500.degree. K. are desired to operate turbines or heat engines, for example. For such purposes then, the heat produced by solar radiation must be concentrated at its intended place of use in order to produce the necessary high temperatures.
The basic principles for accomplishing this are well known; solar radiation is focused or concentrated upon one or more radiation-absorbing elements which absorb a substantial fraction of the incident solar energy and convert it into thermal energy at high temperatures, which thermal energy can then be used for many utilitarian purposes. It is also known to accomplish transfer of the thermal energy from the radiation-absorbing cite to the place of utilization by means of a circulating heat-absorbing fluid. The high temperature of the heat-absorbing fluid may then be used as the source of energy for producing useful work, for example to drive an engine and thus produce useful mechanical work, or to drive a turbine-generator and thus produce useful electrical energy.
It has been proposed to utilize as the radiation-concentrating system a large-area array of spaced-apart flat reflectors supported on the ground about the foot of a tower having a radiation absorber at its top, onto which absorber solar radiation is directed by each appropriately-oriented reflector. However, as the sun executes its daily apparent motion in the sky, the angular orientation of each of the many reflectors must be individually and differently controlled about two axes, and with a high degree of accuracy, a requirement which results in high expense and complexity of the control system. Also, the reflectors themselves must be very accurately configured to assure accurate reflection of radiations onto the remote radiation absorber on the tower. The reflectors must also be spaced apart sufficiently that they do not shade each other for any useful position of the sun, which reduces the effective density of area coverage by the reflectors. Both the reflectors and the tower assembly also present problems of support against wind loads, since wind peaks of 100 m.p.h. must often be accommodated by the support design. Accordingly, while the tower system has some inherent advantages, it also has substantial inherent drawbacks, including those mentioned above.
It has also been proposed to achieve the desired radiation concentration by using one or more trough-like reflectors of paraboloid cross-section, with a liquid-containing radiation-absorbent conduit extending along the line focus of the reflector. Each reflector is rotated about its line focus so as to track the east-west motion of the sun. While perhaps satisfactory for some smaller-scale applications, the system requires individual drives for rotating the reflectors, with some attendant complexity. Also, land covered by the reflectors is no longer available for other uses such as farming.
Thus while these and many other expedients are well known in the prior art, and most are effective to produce some degree of useful heating in response to solar energy, the problem has really been how to collect and transfer the solar energy with minimum cost, least use of land area, and the highest degree of reliability in the particular application involved. Thus the problem is essentially an economic one and, in general, wide usage of solar radiation as a practical source of energy has not come into general usage because of limitations on the practicality of the arrangements thus far known.
One particular possible field of application of solar energy is in those geographic areas, for example the southwest region of the United States, where large-scale irrigation of the land is necessary for plant and/or animal farming. This irrigation process requires large quantities of energy to accomplish the necessary pumping of water; in view of the present and contemplated relative shortage of conventional energy sources such as fossil fuels or electricity, as well as the expense of such fuels, continuance of necessary farm irrigation presents serious problems which are expected to become even more serious in the future.
While the present invention will be described with particular respect to its application in providing energy in suitable form for accomplishing pumping in farm irrigation, it provides improvements which have wide application entirely outside the field of irrigation pumping or the like.
It is therefore an object of the present invention to provide a new and useful method and apparatus for the collection and conversion of solar energy.
Another object is to provide such collection and conversion in a manner which is highly practical, particularly from the viewpoints of cost, reliability and area of land-use required.
Another object is to provide such a method and apparatus which is especially applicable to providing energy in areas utilizing irrigation, and which simultaneously assists in minimizing irrigation water losses through evaporation.